Differential Rotation of Northeastern Part of Southwest Japan

Paleomagnetism of Early to Late Miocene Rocks from Yatsuo Area in Chubu District

抄録

A paleomagnetic study has been carried out on the Miocene volcanic and sedimentary rocks from the Yatsuo area, the northern part of the Chubu district. Stable primary magnetizations are recognized from 8 sites among 36 sites ranging from 17 to 7Ma in age. Eight sites are grouped into two by their declinations; the lower 4 sites show easterly deflected declinations (mean direction: D=12.6°, 1=47.1°, α₉₅=7.0°) and the upper 4 sites show no significant deflection from the axial geocentric dipole field (mean direction: D=-2.5°, I=55.6°, α₉₅=6.6°). This result suggests that the Yatsuo area was subjected to a clockwise rotation about 13° between 15 and 12Ma, possibly synchronous with the rotation of Southwest Japan. The smaller rotation angle than that estimated for Southwest Japan (47°) suggests the differential rotation between the block which contains the Yatsuo area and the main part of Southwest Japan.